1. Technical Field
The present disclosure relates to a radar device.
2. Background Art
A vehicle-mount radar device of the related art is, for example, arranged on a back side of a bumper of a vehicle and can detect a position, a direction, a distance, a velocity, etc., of an object by transmitting a transmission wave that penetrates through the bumper, receiving a reflected wave that is reflected by an object, and analyzing a relationship between the transmission wave and the reflected wave.
Although the bumper is constituted by a member made of a resin or the like that is permeable to electromagnetic waves, depending on a positional relationship between an antenna and the bumper, there may be a case in a pulse radar where a radio wave transmitted from a transmitting antenna is reflected on the bumper and a reflected radio wave is reflected on a radar again, and an object is detected as if there are a plurality of objects.
FIG. 16 is a plan view showing a substrate on which antennas of the radar device of the related art are formed. As shown in FIG. 16, a substrate 10 of a radar device 1A of the related art is provided with a GND (Ground) copper foil section 130 at the center thereof and a plurality of (in FIG. 16, four) antenna units 111 on a right-hand side thereof that are arrayed to form a transmitting antenna 110. Further, a plurality of (in FIG. 16, eight) antenna units 121 are provided on a left-hand side of the GND copper foil section 130 and are arrayed to form a receiving antenna 120.
FIG. 17 is a cross sectional view showing a state where the substrate 10 shown in FIG. 16 is accommodated in a radome 20 and stored at the back side of the bumper of the vehicle. In an example of this diagram, the radome 20 made of a resin having radio wave permeability is arranged to cover a surface of the substrate 10 on which the antennas are formed. The radar device 1A is arranged on the back side of a bumper B.
In such a state, as indicated by a broken line, a part of the radio wave transmitted from the transmitting antenna 110 is reflected by the bumper B, and then is incident on the GND copper foil section 130 and reflected thereon. Then, the part of the radio wave is reflected again by the bumper B, and thereafter is incident on the receiving antenna 120.
FIG. 18 is a diagram showing signals that are transmitted and received by the radar device 1A, and specifically shows a relationship between a transmission signal, reflected waves from a bumper, and a received signal which is a reflected wave from an object. In an example of this figure, the transmission signal is transmitted from the transmitting antenna 110 in a period T1, and the reflected wave from the bumper B is received several times (in this example, four times) in a subsequent period T2, while being attenuated. In a subsequent period T3, the reflected wave from the object (e.g., another vehicle) is received.
In this manner, when the reflected wave from the bumper B is received, there may be a case where the radar device 1A falsely detects it as an object. In the example of FIG. 18, the reflected waves from the bumper B and the reflected wave from the object are not temporally overlapped, but, in a case where they overlap, the reflected waves from the bumper B becomes a noise and the radar device 1A cannot detect the object accurately.
In the following cases, the reflected wave from the bumper B could obstruct the detection of the object. For example, in one case, a part of the radio wave transmitted from the transmitting antenna 110 is reflected on the bumper B, and then is incident on the GND copper foil section 130 and reflected thereon. Then, the part of the radio wave penetrates the bumper B, and is reflected by an object. Then, the part of the radio wave penetrates the bumper B again, and is incident on the receiving antenna 120. In another case, the radio wave transmitted from the transmitting antenna 110 penetrates the bumper B, and is reflected by an object. Then, the part of the radio wave penetrates the bumper B again, and is incident on the GND copper foil section 130 and reflected thereon. Then, the part of the radio wave is reflected on the bumper B, and is incident on the receiving antenna 120. The path of the reflected wave is not limited to the above, and there may be a case where the aforementioned reflections occur in a combined manner.
Accordingly, in order to solve such a problem, in the related art, there is a technique of reducing an influence of the bumper on a transmission signal by providing the bumper with an uneven geometry (Japanese Laid-Open Patent Publication No. 2008-249678).
There is also a technique of reducing an influence of a member such as a bumper, by controlling a modulation frequency of the transmission signal in such a manner that a reflection loss from the member such as the bumper is minimized (Japanese Laid-Open Patent Publication No. 2006-317162).
Further, there is also a technique in which a reflector is provided around an aperture in an array antenna unit, and an amount of shift of a beam or a null point is reduced by an existence of a radome (Japanese Laid-Open Patent Publication No. 2010-109890).
With the technique described in Patent Literature 1, since it is necessary to form a complicated geometry at the back side of the bumper, there is a drawback that a production cost of the bumper is increased.
With the technique described in Patent Literature 2, since the transmission frequency is adjusted, there is a drawback that it is not applicable to a radar having a fixed transmission frequency.
With the technique described in Patent Literature 3, there is a drawback that it is not possible to reduce an influence of reflection at an aperture of an array antenna.
Accordingly, the present disclosure relates to providing a radar device that can reduce an influence of a structure, such as a bumper that is constantly arranged on a transmission path, on a transmission signal or a received signal.